Apple’s engineers have explained how the iPhone Duo spreads heat from its A20 Pro chip across both halves of the foldable. In an exclusive interview with PCMag, Apple’s vice president of silicon engineering Dan Murray and senior manager of thermal product design Banafsheh Barabadi said a flexible graphite pipe runs through the hinge to transfer heat between the two sides.

Because the Duo doubles in thickness when closed, Barabadi called its thermal design “one of the most technically challenging aspects of our design”. The graphite pipe increases the surface area available for heat dissipation and had to be co-engineered by the thermal and mechanical teams, as it must survive many hinge cycles while keeping its thermal connectivity and structural integrity. The Duo also uses its own vapour chamber, thinner than the one in the iPhone 18 Pro, which floats in the middle of the device rather than forming part of its support structure.

Four pillars of the A20 Pro cooling design

Most of the thermal work applies to all three new phones. Murray said the A20 Pro moves away from the package-on-package design used in earlier iPhone chips: the DRAM now sits next to the processor in a wafer-level multichip module (WMCM) package rather than on top of it, which gives the chip a direct path to the vapour chamber.

Barabadi described four pillars: that direct silicon access; a new “metal over foam” material coupling the chip to the vapour chamber, which she said took “months of development to get the material properties exactly right”; a vapour chamber with three times the surface area of the one in the iPhone 17 Pro, which in the iPhone 18 Pro and Pro Max also serves as the phone’s central structural plane; and a nanotube copper plate with a graphite layer on the back of the display to spread heat. “When we combine these four pillars together, it meaningfully improves the thermal performance across every metric,” she said, adding that Apple achieves 35 per cent higher sustained GPU performance than the iPhone 17 Pro.

AppleInsider notes that the metal-over-foam layer was already spotted in an iPhone 18 Pro teardown, where it was described as “thermal chainmail”.

The iPhone Duo launches on 23 October.